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<html lang="en">
<head>
    <meta charset="UTF-8">
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    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
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<body>
    
</body>
<script>

var num = 3000;

var jx = prompt('请输入绩效工资');

var num1 = parseInt(jx);

var res = num + num1;
 
alert(res);

// 转换成数字
// Number()
// 转换成整数
// parseInt()
// 转换成小数
// parseFloat()
</script>
</html>